RAIDing flash drives

I would not suggest using a USB 2.0 raid method as the transfer rate between that and an internal mounted hard drive (SATA or SAS) is significantly slower. Combined with the fact that you are using a USB HUB, it would make the transfer rate even slower thus defeating the purpose of a RAID setup.

Building a raid out of a bunch of cheap usb thumb drives is a great idea. A 'must read' on this topic can be found here: http://analogbit.com/node/4

To summarize, up to six USB flash drives are needed to saturate usb bandwidth in most of the use cases. Lots of USB flash drive with low write speed are actually doing wear leveling internally (ex: Sandisk Cruzer Blade 4GB stuck at 4MB/s for this purpose). With only one flash drive, write speed is about 4 to 10 MB/s. With six flash drives in RAID 0, the write speed is as high as an external hard disk: no tradeoff is made between data safety versus write speed performance with that kind of setup.

About the use cases:

• cheap storage possible
• low power consumption
• low heat
• noiseless operation
• no data safety vs performance tradeoff
• size can be dynamically expanded

PS: I personally use a RAID0 made of seven Sandisk Cruzer Blade 32GB and a D-Link HUB H7 plugged on a OpenWrt router that runs 24/7. Total cost lower than a 256GB SSD and a 2.5" external HDD enclosure.